Fourth
From The Stargate Omnipedia
Female humanoid Replicator, the fourth to emerge from the intelligence of the Replicators after they took over the Asgard planet Halla. She is one of the first four who got the chance to enter the minds of SG-1 in the hopes of gaining information about the planets in the team's home galaxy.
After being trapped within a time dilation device Fourth was apparently destroyed when the Asgard converted Halla's star into a singularity to rid themselves of the Replicator threat for good.
DETAILS
PLAYED BY - Rebecca Robbins
FIRST APPEARED - Unnatural Selection
KEY EPISODE
Unnatural Selection - Fourth is one of the Replicator androids on Halla who corral SG-1 and enter their minds, searching for strategic information.